Cancer Risk Factors in Ontario. Dusts and Fibres

Transcription

1 Cancer Risk Factors in Ontario Dusts and Fibres

2 dusts ANd fibres risk factor/exposure Cancer The context where high risks were reported Magnitude of risk* Strength of evidence a Asbestos Larynx Occupational 1.2 a (all forms) Lung Occupational 2 5 a,b Environmental Mesothelioma Occupational Sufficient Environmental Ovary Occupational c,d Colon and rectum Occupational Pharynx Occupational Limited Stomach Occupational Silica dust, crystalline Lung Occupational a Sufficient (in form of quartz or crystobalite) Wood dust Sinonasal Occupational 2 50 e,f Nasopharynx Occupational a Sufficient Sources: a IARC, 2012; b Lenters et al., 2011; c Reid et al., 2009; d Camargo et al., 2011; e Demers et al., 1995; f IARC, 1995 *Relative risk (RR) estimate for persons exposed vs. unexposed....magnitude of risk not shown in table if strength of evidence could not be accurately estimated or is limited. The vast majority of mesotheliomas are the result of occupational exposure to asbestos, the remaining cases are likely the result of the environment. The precise magnitude of risk is difficult to determine. ASBeSTOS (ALL forms)» Asbestos is a commercial term for a group of six fibrous minerals made of silicon and magnesium, including amphibole minerals (actinolite, amosite, anthophyllite, crocidolite, tremolite) and serpentine minerals (chrysotile), that are found naturally in soil and rocks. 108,123» Asbestos fibres have several desirable properties, including resistance to heat, durability and strength, that have led to their use in a wide range of industrial applications, most frequently involving insulation and friction materials (e.g., brake pads and shoes). 124» Asbestos fibres are released into the environment from the weathering or mining of natural asbestos deposits and when asbestos-containing products are worn down or damaged. 124 The primary route of human exposure is inhalation of these airborne asbestos fibres. 124» Exposure is most likely to occur in occupational settings. Workers in several industries may have been or are currently exposed to asbestos, including those involved in asbestos mining, manufacturing, construction and transportation, as well as in the maintenance and remediation of asbestos containing structures. 125 Cancer Risk Factors in Ontario: Evidence Summary 33

3 There is consistent evidence that exposure to asbestos causes mesothelioma, and cancers of the lung, larynx and ovary. 124 There is a clear dose-response relationship between asbestos exposure and lung cancer risk. 126 A meta-analysis has shown that people in the highest exposed groups of workers (e.g., miners and insulators) are between 2 and 5 times more likely to develop lung cancer. 126 The impact of different asbestos fibre types and sizes on lung cancer risk remains unclear. 124 It is uncertain whether there is an increased risk for lung cancer at low levels of asbestos exposure. 124 The magnitude of risk from environmental exposure is too difficult to determine based on the existing literature. Mesothelioma, in contrast, can occur at low levels of exposure to asbestos as demonstrated by cases that occur as a result of environmental exposures. This is also indicated by studies where household members of asbestos workers have been found to be at risk of mesothelioma from contact with asbestos carried into the home (i.e., via hair, shoes and clothing) from their household member s workplace. 127,128 The vast majority of mesothelioma cases are the result of occupational exposure to asbestos; many of the remaining cases are likely the result of environmental exposure. Exposure to materials that are contaminated with asbestos is also associated with an increased lung cancer risk. For instance, vermiculite mined in Libby, Montana was contaminated with amphibole fibres (asbestos) and caused increased mesothelioma and lung cancer rates. 124 This asbestos-contaminated vermiculite was shipped to other areas, including Ontario and other Canadian provinces. Smoking does not affect the risk of mesothelioma; however, smokers who are exposed to asbestos have a greatly increased risk of developing asbestos-related lung and laryngeal cancer. 124 A meta-analysis found that, after adjusting for alcohol and tobacco consumption, people exposed to asbestos have an approximately 20% higher risk of laryngeal cancer. 123 Higher risks of asbestos-related laryngeal cancer have also been observed in certain populations. 124 There is evidence of a dose-response relationship for cumulative asbestos exposure and laryngeal cancer. 124 A dose-response relationship exists between asbestos exposure and ovarian cancer risk; 124 some studies have found that women living near asbestos facilities have a higher risk of ovarian cancer Women with occupational asbestos exposure have an approximately 30% 80% increased risk of ovarian cancer. 130,131 There is limited evidence for an association between asbestos exposure and cancers of the colon and rectum, pharynx and stomach. 132 Individuals with any exposure to asbestos are 50% more likely to develop pharyngeal cancer and 10% 40% more likely to develop colorectal or stomach cancer 123,124 compared to people with no exposure. The biologic mechanisms by which asbestos can induce cancer include impaired fibre clearance leading to macrophage activation, inflammation, generation of reactive oxygen and nitrogen species, tissue injury, genotoxicity, aneuploidy and polyploidy, epigenetic alteration, activation of signaling pathways, and resistance to apoptosis. 132 A study has also found that the release of the HMGB1 protein triggers a chronic inflammatory response in human mesothelial cells, which can lead to carcinogenesis Cancer Risk Factors in Ontario: Evidence Summary

4 SILICA dust, CrYSTALLINe (IN THe form Of QUArTZ Or CrISTOBALITe)» Silica is one of the most common minerals, naturally occurring in both crystalline and amorphous forms. 124 The most common type of crystalline silica is α-quartz; other common types include cristobalite and tridymite. 124» Crystalline silica is found naturally in rocks, soil, sands, acid volcanic rocks, some bentonite clays and in diatomateous earth, and can be produced through the conversion of amorphous forms of silica in the presence of heat. 124» The main categories of commercial silica products are sand and gravel (used in manufacturing glass, ceramics, foundry and abrasives), quartz crystals (used in jewelry, electronics and optical components), and diatomateous earth (used in filtration as fillers in and as carriers for pesticides and other commercial products, such as cleaners). 124» Workers in industries and occupations involving the movement of earth (e.g., mining, farming), the disturbance of silica-containing products (e.g., demolition of concrete) and the handling or use of sand or other silica-containing products (e.g., foundry processes) are considered to be at high risk of silica exposure, 124 with inhalation the primary route of exposure.» Exposure in the general population is most likely to occur during the use of commercial products containing quartz (e.g., cleansers, cosmetics, art clays and glazes, pet litter, talcum powder, caulk, paint and mortar), with inhalation as the primary route of exposure. 124 There is consistent evidence demonstrating an association between crystalline silica (in the form of α-quartz and cristobalite dust) and lung cancer, with a clear dose-response relationship. 124 Exposure to silica dust increases lung cancer risk fold, 124,134 with higher risks from higher exposure levels. 124 The established biologic mechanisms for carcinogenesis include impaired particle clearance leading to macrophage activation and persistent inflammation. 132 wood dust» Wood dust is generated during the processing of wood (e.g., via sawing, sanding). It can come from softwood trees, which are mainly conifers, or hardwood trees, which are primarily deciduous trees in North America. 124» Wood dust exposure is generally highest during the manufacturing of wood furniture and cabinets, especially during the process of machine-sanding. 124 The primary route of exposure is inhalation of the dust.» Since the industrial revolution, woodworking machines have increased in efficiency, increasing both production, and the generation of more and finer wood dust. 124 Cancer Risk Factors in Ontario: Evidence Summary 35

5 There is consistent evidence that exposure to wood dust causes sinonasal and nasopharyngeal cancer. 124 For sinonasal adenocarcinoma, there is strong evidence for a dose-response relationship. Depending on exposure level and wood dust type, risk ranges from 2 50 times that of the general population. 135,136 The highest risks for sinonasal adenocarcinoma have been observed for people exposed to high levels of hardwood dust and very high relative risks have been primarily observed in European studies. 124,135 People in wood-related occupations or who are exposed to wood dust are at times increased risk of nasopharyngeal cancer, with insufficient evidence for a dose-response relationship. 124 The biologic mechanisms by which wood dust causes cancer have not been established. 124 OTHer dusts ANd fibres There is sufficient evidence that exposure to erionite (a fibrous zeolite similar to asbestos) causes mesothelioma. 124 Environmental and epidemiological evidence is mainly derived from high-risk populations where erionite is most prevalent (e.g., Turkey). 137,138 In occupations with high exposure to leather dust (e.g., boot, shoe or other leather workers), there is sufficient evidence of increased risk of sinonasal cancer. 124 The evidence has come primarily from European studies Cancer Risk Factors in Ontario: Evidence Summary